The goal of a series of listening tests was to better isolate the principal dimensions of timbre, using a wide range of timbres and converging psychophysical techniques. Expert musicians and nonmusicians rated the timbral similarity of three sets of pitched and percussive instruments. Multidimensional scaling analyses indicated that both centroid and rise time comprise the principal acoustic factors across all stimulus sets and that musicians and nonmusicians did not differ significantlyin their weighting of these factors. Clustering analyses revealed that participants also categorized percussive and, to a much lesser extent, pitched timbres according to underlying physical-acoustic commonalties. The findings demonstrate that spectral centroid and rise time represent principal perceptual dimensions of timbre, independent of musical training, but that the tendency to group timbres according to source properties increases with acoustic complexity.Timbre is a complex and multidimensional perceptual attribute most closely associated with a sound's "quality" or "texture." Most studies of auditory timbre over the past three decades have employed some form ofmultidimensional scaling (MOS) algorithm to characterize its attributes. The principal goal of such research is to discover the mapping between the physical features of the signal and the mental representation of their corresponding timbral attributes by the listener. MDS algorithms usually make few a priori assumptions about the structural properties of psychological data and are therefore particularly appropriate for the study of complex stimuli whose underlying perceptual or psychophysical characteristics are poorly understood. One assumption is that timbre can be represented by a small number ofcontinuous, orthogonal dimensions. An additional assumption underlying past studies has been that the timbres of two or more sounds should be compared under controlled conditions in which the pitch, loudness, and duration ofsuch sounds have been equalized in order to control for possible interactions between these parameters and timbre.Consistent reports have emerged in the literature regarding the principal acoustic determinants of timbre perception. For example, using synthetic tones with determined sets of tim bra I attributes, Miller and Carterette (1975) reported that the number of harmonics comprising

When we examine objects haptically, do we weight their local and global features as we do visually, or do we place relatively greater emphasis on local shape? In Experiment 1, subjects made either haptic or visual comparisons of pairs of geometric objects (from a set of 16) differing in local and global shape. Relative to other objects, those with comparable global shape but different local features were judged less similar by touch than by vision. Separate groups of subjects explored the same objects while wearing either thick gloves (to discourage contour-following) or splinted gloves (to prevent enclosure). Ratings of similarity were comparable in these two conditions, suggesting that neither exploratory procedure was necessary, by itself, for the extraction of either local or global shape. In Experiment 2, haptic exploration time was restricted to 1, 4, 8, or 16 sec. Limiting exploration time affected relative similarity in objects differing in their local but not their global shape. Together, the findings indicate that the haptic system initially weights local features more heavily than global ones, that this differential weighting decreases over time, and that neither contour-following nor enclosure is exclusively associated with the differential emphasis on local versus global features.In recent years, considerable effort in haptic research has been directed toward characterizing spatial processing capabilities. The haptic system combines both cutaneous and kinesthetic information to construct an internal representation of external objects and spatial configurations, using both bottom-up processes that convey topographical input concerning spatial layouts and top-down processes that optimize search procedures directed at specific types of spatial features. Two theoretical perspectives can be discerned in the literature: The first compares haptic with visual spatial processing, seeking perceptual equivalences (or nonequivalences) between touch and vision (e.g., Brown & Brumaghim, 1968;Garbin & Bernstein, 1984); the second highlights the role of non spatial cues (e.g., texture, hardness, temperature) and task-driven exploratory procedures, such as prototypical hand movements, in haptic form perception, assuming the existence of separate processing channels for touch and vision (e.g., Klatzky & Lederman, 1993).Several researchers have reported a strong equivalence between visual and haptic form perception. Brown and Brumaghim (1968) found that haptic and visual ratings of complexity of stimuli drawn from a set of 1,000 2-D

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